The present invention relates to a liquid droplet ejection apparatus, a method for forming a pattern, and a method for manufacturing an electro-optic device.
A procedure for manufacturing a color filter or an alignment film, which are employed in a liquid crystal display, involves a liquid phase process. In the liquid phase process, liquid containing material for forming thin films is ejected onto a film forming surface, or an ejection target surface. The liquid is then dried on the film forming surface so as to provide the thin films.
Specifically, an inkjet method is employed in the liquid phase process. In the inkjet method, the liquid is ejected onto the film forming surface as droplets and the droplets are dried to form the thin films. The inkjet method reduces the consumption amount of the liquid, compared to other types of liquid phase processes (such as a spin coating method or a dispenser method). Further, the inkjet method adjusts the positions at which the thin films are formed more accurately than the other methods.
Using the inkjet method, a thin film may be formed over a relatively wide range on a film forming surface as in a large-sized liquid crystal substrate. In this case, the substrate is repeatedly scanned with respect to a liquid droplet ejection head, which ejects liquid droplets in multiple cycles. The droplets from one of the cycles dry earlier than those from a following cycle. This creates a boundary (surface unevenness) between the droplets from different cycles, thus lowering the quality of an image displayed by the liquid crystal display.
In order to avoid formation of such boundaries (surface unevenness) between droplets that have been ejected at different timings, various solutions addressed to the inkjet method have been proposed. For example, as described in Japanese Laid-Open Patent Publication No. 2004-347694, a plurality of liquid droplet ejection heads are aligned in a direction (a sub scanning direction) perpendicular to a scanning direction of a substrate. Ejection nozzles, which eject liquid droplets, are spaced at uniform pitches with respect to the sub scanning direction. Thus, in a single cycle of scanning, which is performed in the scanning direction, the liquid droplets are continuously ejected onto an entire ejection target surface, thus avoiding the formation of the boundaries between the droplets.
However, as shown in FIG. 17A, in order to adjust the pitch of the ejection nozzles N to a value equal to a constant nozzle pitch Pn with respect to the sub scanning direction (direction X), the nozzles N of the liquid droplet ejection head FH1 are arranged offset from the nozzles N of the adjacent liquid droplet ejection head FH2 in the main scanning direction (direction Y) by a distance corresponding to the width (the head width Wh) of each liquid droplet ejection head FH1, FH2 in direction Y. Therefore, microdroplets ejected from the liquid droplet ejection head FH1 and microdroplets ejected from the liquid droplet ejection head FH2 are received by the substrate at different timings corresponding to the head width Wh.
Specifically, if a droplet 103 and a droplet 104, which have been received by the substrate at different timings, flow to overlap each other, a projected portion FDT is formed at a boundary between the droplet 103 and the droplet 104 on a film forming surface 102 of the substrate 101, with reference to FIG. 17B. The thickness of the projected portion FDT is several hundreds of nanometers to several micrometers. If the droplet 103 does not overlap the droplet 104, an area having smaller droplet thickness or an empty area may be caused at the boundary between the droplet 103 and the droplet 104.
This varies the thickness of the droplets or the thickness of the thin films at the boundaries between the droplets that have been ejected at different timings, thus lowering the quality of an image displayed by the liquid crystal display.